The goal of this proposal is to understand the genes required for maleness in Drosophila melanogaster. The first set of studies is directed at finding additional genes in the fruitless (fru) branch of the sex-determination pathway. This branch has been implicated in the development and/or maintenance of male specific courtship behavior as well as the development of male specific Muscle of Lawrence (MOL). Using correct MOL development as a visual tool, various genes will be expressed in the nerves that are critical for MOL development. If the expression of a gene in MOL neurons, in a fru mutant background, rescues MOL development then that gene will be considered as part of the fru pathway. IN addition, a genetic screen will be performed to identify suppressor mutations of the original fru1 mutation. The second set of experiments is directed at understanding cues males us to identify potential mates. A locus, fruitless stimulation factor (fsf), when mutated gives rise a mutant phenotype of males which are vigorously courted by other males. Normal males as a rule are not strongly courted by other normal males. Current studies have pinpointed the region that harbors the mutation. Database analysis has demonstrated that two transcribed regions or separate sets of EST's are located very near the mutation. Future experiments will be directed at determining which of t he two potential transcription units if the gene referred to as fsf as well as the role of the gene in the establishment of maleness.